VARIETIES. 
391 
upper  part  of  the  chamber  (or  gas  producer)  with  the  former  hydro-carbons. 
The  water,  which  is  purposely  introduced  at  the  bottom  of  the  arrangement, 
is  first  vaporized  by  the  heat,  and  then  decomposed  by  the  ignited  fuel,  and 
re-arranged  as  hydrogen  and  carbonic  oxyd  ;  and  only  the  ashes  of  the 
coal  are  removed  as  solid  matter  from  the  chamber  at  the  bottom  of  the 
fire-bars. 
"  These  mixed  gases  form  the  gaseous  fuel.  The  nitrogen  which  entered 
with  the  air  at  the  grate  is  mingled  with  them,  constituting  about  a  third 
of  the  whole  volume.  The  gas  rises  up  a  large  vertical  tube  for  twelve  or 
fifteen  feet,  after  which  it  proceeds  horizontally  for  any  required  distance, 
and  then  descends  to  the  heat  regenerator,  through  which  it  passes  before 
it  enters  the  furnaces.  A  regenerator  is  a  chamber  packed  with  fire-bricks, 
separated  so  as  to  allow  of  the  free  passage  of  air  or  gas  between  them. 
There  are  four  placed  under  a  furnace.  The  gas  ascends  through  one  of 
these  chambers,  whilst  air  ascends  through  the  neighboring  chamber,  and 
both  are  conducted  through  passage  outlets  at  one  end  of  the  furnace, 
where  mingling,  they  burn,  producing  the  heat  due  to  their  chemical 
action.  Passing  onward  to  the  other  end  of  the  furnace,  they  (i.e.,  the 
combined  gases)  find  precisely  similar  outlets,  down  which  they  pass  ;  and 
traversing  the  two  remaining  regenerators  from  above  downward,  heat  them 
intensely,  especially  the  upper  part,  and  so  travel  on  in  their  cooled  state 
to  the  shaft  or  chimney.  Now  the  passages  between  the  four  regenerators 
and  the  gas  and  air  are  supplied  with  values  and  deflecting  plates,  which 
are  like  four  way-cocks  in  their  action  ;  so  that  by  the  use  of  a  lever  these 
regenerators  and  air-ways,  which  were  carrying  off  the  expended  fuel,  can 
in  a  moment  be  used  for  conducting  air  and  gas  into  the  furnace;  and 
those  which  just  before  had  served  to  carry  air  and  gas  into  the  furnace 
now  take  the  burnt  fuel  away  to  the  stack.  It  is  to  be  observed,  that  the 
intensely-heated  flame  which  leaves  the  furnace  for  the  stack  always  pro- 
ceeds downward  through  the  regenerators,  so  that  the  upper  part  of  them 
is  most  intensely  ignited,  keeping  back,  as  it  does,  the  intense  heat:  and 
so  effectual  are  they  in  this  action,  that  the  gases  which  enter  the  stack  to 
be  cast  into  the  air  are  not  usually  above  300°  F.  of  heat.  On  the  other 
hand,  the  entering  gas  and  air  always  pass  upward  through  the  regene- 
rators, so  that  they  attain  a  temperature  equal  to  a  white  heat  before  they 
meet  in  the  furnace,  and  there  add  to  the  carried  heat  that  due  to  their 
mutual  chemical  action.  It  is  considered  that  when  the  furnace  is  in  full 
order,  the  heat  carried  forward  to  be  evolved  by  the  chemical  action  of 
combustion  is  about  4000°,  whilst  that  carried  back  by  the  regenerator  is 
about  3000°,  making  an  intensity  of  power  which,  unless  moderated  on 
purpose,  would  fuse  furnace  and  all  exposed  to  its  action. 
"  Thus  the  regenerators  are  alternately  heated  and  cooled  by  the  out- 
going and  entering  gas  and  air,  and  the  time  for  alternation  is  from  half 
an  hour  to  an  hour,  as  observation  may  indicate.  The  motive  power  on 
the  gas  is  of  two  kinds  ;  a  slight  excess  of  pressure  within  is  kept  up  from 
